1. Field of the Invention
This invention relates to image-forming apparatuses, in particular, to a sheet discharge unit or a sheet discharge tray provided for loading a printed sheet of paper.
2. Description of the Related Art
Conventionally, an image-reading unit (scanner) and an image-forming unit are separately arranged above and below. The image-reading unit (scanner) is arranged above the image-forming unit having an image-fixing unit and the like. The image-reading unit (scanner) and an image-forming unit are separately arranged so that the sheet discharge tray may not protrude from side faces of the image-forming unit. The sheet discharge tray is used for loading printed sheets of paper. Thus arranged image-reading unit and the image-forming unit forms a space for providing the sheet discharge unit.
Recently, with the background of advancements in the complex capabilities of the image-forming apparatus, the place where the discharged sheet is loaded or ejected can be selected for every use or every user. In many cases, multiple sheet discharge trays are provided.
Japanese Patent Application Publication No. 2001-63898 (hereinafter referred to as Document 1), Japanese Patent Application Publication No. 2001-109211 (hereinafter referred to as Document 2), and Japanese Patent Application Publication No. 2002-308511 (hereinafter referred to as Document 3) propose improvements in the sheet discharge unit, which is arranged between the image-reading unit and the image-forming unit in the image-forming apparatus.
Document 1 describes an image-forming device having a space part formed by an image-reading part and an image-forming part. A sheet on which an image is formed is discharged onto the space part. The proposals of Document 1 are improvements in the visibility and the easy take out of the discharged sheet. Specifically, the multiple trays for storing the discharged sheets are inclined to be lowered on the sheet discharge direction tip side.
Document 2 describes the image forming device having a main body and an optical unit. Even if the optional unit is attached on a space between the main body and the optical unit, the space on a sheet receiving tray is not narrowed. Specifically, the optical unit and the main body can be separated. Positioning members to determine attachment positions in a horizontal direction are respectively provided on the main body and the optical unit so that the optional unit can be attached between the optical unit and the main body.
Document 3 proposes to stack a large number of sheets on a second delivery sheet stacking means. Specifically, the second delivery sheet stacking tray, which is provided above a first delivery sheet stacking tray, is supported by two side walls.
Proposals made by the above-mentioned Documents 1 through 3 commonly include multiple paper receiving trays or sheet stacking trays, which are provided above and below in a layer structure. Arrangements and attachment methods of the above-mentioned layer structure are different according to the purpose. However, the proposals of the Documents 1 through 3 also include a common mechanism, in which sheets pass through a fixing device provided below and discharge rollers provided one above the other. Then, the sheets of papers are sorted into the paper receiving trays and sheet stacking trays. In addition, the paper receiving trays or sheet stacking trays are provided in a layer structure one above the other and parallel to each other, and have common attachment angles and curvatures.
In the fixing device described in each of the above-mentioned Documents 1 through 3, a toner image is transferred to a sheet. The sheet passes between a heating roll and a pressure roll and heat and pressure are applied to the sheet. Toner is melted by heat and pressed on the sheet. Thus, fixing is completed. The sheet, having passed through the fixing device, is heated and easy to get rolled, after passing through the rolls in the fixing device. In particular, the sheet gets curled easily when discharged from a discharge roll provided closest to the fixing device, namely, the discharge roll arranged immediately above the fixing device. A description will be given of the curled sheet with reference to FIG. 1.
FIG. 1 schematically illustrates a sheet discharge portion. The sheet discharge portion includes discharge rolls 101, 102, and 103, provided above a fixing unit 100. The discharge rolls 101, 102, and 103 are arranged from the bottom. As is obvious from FIG. 1, a largest shoot curvature is a shoot curvature ρ3 of the sheet discharged from the discharge roll 103, which is provided furthest from the fixing unit 100. A second largest shoot curvature is a shoot curvature ρ2 of the sheet discharged from the discharge roll 102. The smallest shoot curvature is a shoot curvature ρ1 of the sheet discharged from the discharge roll 101, which is provided closest to and immediately above the fixing unit 100.
The sheet discharged from the discharge roll 101 passes through the fixing unit 100, and is loaded onto a sheet-receiving unit 104 in a shortest time. The sheet-receiving unit 104 has a shortest path from the fixing unit 100. In this case, the shortest time is allowed for cooling down the heat applied to the sheet when the sheet passes through the fixing unit 100. In addition to the smallest shoot curvature ρ1 when the sheet passes through the discharge roll 101, the sheet discharged from the discharge roll 101 gets curled most easily, and the sheet loaded onto the sheet-receiving unit 104 gets curled easily as a roll.
As described above, if the discharged sheet is curled, a stacking state on the sheet-receiving unit will adversely be affected. As examples of adverse affects, the discharged sheets are not piled up uniformly, or the sheets already loaded on the sheet-receiving unit are sequentially pushed out by the sheets newly discharged one by one.
Proposals made by Documents 1 through 3 commonly include multiple paper receiving trays or sheet stacking trays, which are provided above and below in a layer structure. Arrangements and attachment methods of the above-mentioned layer structure are different according to the purpose. However, the proposals of the Documents 1 through 3 are not made to solve the above-mentioned problem, that is, the discharged sheet easily gets curled. Proposals made by Documents 1 through 3 do not intend to solve the problem of the curled discharge sheet.